The present invention generally relates to the field of integrated circuit technology, and more specifically the invention relates to a monolithically integrated microwave frequency high power amplifier device.
Power amplifiers for many new modulation techniques, especially those applied in 3G base stations like CDMA and multi-carrier techniques, require high linearity together with reasonable power efficiency. A very common approach is to use feed forward power amplifiers, an example of which being illustrated in FIG. 1. The bias network is simplified using large inductors for DC feed and large capacitors for DC block.
To achieve high power it is practical to form a transmitter from some kind hierarchical elements such as transistor fingers, cells, packages or amplifiers that can be used together by adding power from each of the elements at one level to an element at next level.
Two methods are frequently used today: parallel coupling and power combining.
The simplest method is to just connect the elements in parallel using low resistance wires. This works fine as long as the current distribution is uniform. Unfortunately this is not always the case due to manufacturing process variations, asymmetries in the design, or failure of single elements.
The more sophisticated way, to use power combining, is very robust and allows all these kinds of variations and failures without resulting in a total breakdown of the transmitter. Power combiners must be used in many cases because there are no other alternatives.
In research laboratories many new implementations of old concepts like Doherty, Chireix and Kahn have been tested. A schematic of the classic Doherty amplifier is illustrated in FIG. 2.
The main problem with feed forward and switching techniques is the low power efficiency.
The Doherty, Chireix and Kahn amplifiers fulfill the desired specifications but are very difficult to realize with the spread typically occurring in electrical parameter data.
Further, they all rely on power combiners, which is not particularly area efficient.
Thus, it would be advantageous to provide an integrated microwave frequency high power amplifier device that has high linearity and high power efficiency, that occupies less area than a prior art power amplifier, and/or that can be fabricated in any MOS process without the need of additional processing steps.